Hydrophone tested for Samudrayaan

Chennai: Just a few months before India's manned submersible Matsya 6000 undergoes integrated testing, city-based National Institute of Ocean Technology (NIOT) has successfully tested an underwater communication system, or ‘underwater telephone', at Kerala's Idukki dam. The system, which works on acoustic sound waves, will enable real-time communication between researchers several kilometres deep in the ocean and those aboard the mothership.The submersible will undergo integrated testing in early 2026 as part of the Samudrayaan mission under the Deep Ocean Mission.In the Idukki test, hydrophones were suspended five metres below the surface from two separate boats stationed 5.5 km apart. One boat remained stationary, while the other moved away. Hydrophones were also tested at varying depths as researchers on board communicated through the acoustic transmitter and receiver. The location was chosen for its long, straight stretch, reservoir and logistical support from the Naval Physical and Oceanographic Laboratory (NPOL), which provided boats and assistance. The underwater telephone was initially developed and tested in laboratory conditions at NIOT."We are able to flawlessly communicate and hear between the boats," said NIOT director Balaji Ramakrishnan, confirming the clarity achieved over long horizontal distances. "We wanted to understand the device's maximum range by testing in a controlled environment like Idukki dam. The next step will be to test in actual ocean conditions."In the open sea, the system will be tested for vertical range at depths of 1,000m-2,000m, where changing temperature, conductivity, salinity, and pressure may affect sound wave propagation.Other critical subsystems are also undergoing independent testing. An underwater positioning system and a side-scan sonar were tested at Idukki. Life support systems were tested and optimised to reduce space inside the titanium spherical hull where researchers will be seated, leaving more room for scientific payloads. NIOT researchers are also in discussions with Norwegian certification agency Det Norske Veritas, whose team, including members from Norway, Germany, and India, is in the city to evaluate Matsya 6000's components and safety standards.